Priming the NoMorePly Fibre Cement boards is always a good thing for a number of reasons:

It makes the boards waterproof rather than water-resistant.
It enhances the bond strength between the board and the adhesive.
It consolidates any dust on the surface of the boards.
You will need to prime both sides of the boards when using cement adhesive to fix the boards to a solid wall or floor.

NoMorePly Tilers Primer should be diluted 1 part primer & 3 parts water before use. Using it neat will not be an advantage.